Apparatus and methods for procedures related to the electrophysiology of the heart

ABSTRACT

Methods and apparatus are disclosed for use in procedures related to the electrophysiology of the heart, such as identifying or evaluating the electrical activity of the heart, diagnosing and/or treating conditions associated with the electrophysiology of the heart. An apparatus having thermocouple elements of different electromotive potential conductively connected at a junction is introduced into the interior of the heart and a section of heart tissue is contacted with the junction. An electrical current is passed through the thermocouple elements to reduce the temperature of the junction in accordance with the Peltier effect and thereby cool the contacted heart tissue. The effect of the cooling may be monitored and, if desired the section of heart tissue may be treated.

This application is a continuation-in-part of application U.S. Ser. No.670,177 filed on Jun. 20, 1996, now U.S. Pat. No. 5,755,663, which is adivision of U.S. Ser. No. 294,478, filed on Aug. 19, 1994, now U.S. Pat.No. 5,529,067.

FIELD OF INVENTION

The present invention relates generally to methods and apparatus fordiagnosing or treating electrophysiological conditions of the heart.More specifically, the present invention relates to novel methods andapparatus for evaluating the electrical activity of the heart, foridentifying an electrophysiological source of heart arrhythmia, and fortreating heart arrhythmia.

BACKGROUND ART

As is well known, the human heart has four chambers for receiving bloodand for pumping it to various parts of the body. In particular, the twoupper chambers of the heart are called atriums, and the two lowerchambers are called ventricles.

During normal operation of the heart, oxygen-poor blood returning fromthe body enters the upper right chamber known as the right atriumthrough the superior vena cava and inferior vena cava. The right atriumfills with blood and eventually contracts to expel the blood through thetricuspid valve to the lower right chamber known as the right ventricle.Contraction of the right ventricle ejects the blood in a pulse-likemanner from the right ventricle to the pulmonary artery which dividesinto two branches, one going to each lung. As the oxygen-poor bloodtravels through the lungs, it becomes oxygenated (i.e. oxygen-rich).

The oxygenated blood leaves the lungs through the pulmonary veins andfills the upper left chamber of the heart known as the left atrium. Whenthe left atrium contracts, it sends the blood through the mitral valveto the lower left chamber called the left ventricle. Contraction of theleft ventricle, which is the stronger of the two lower chambers, forcesblood through the main artery of the vascular system known as the aorta.The aorta branches into many smaller arteries and blood vessels thateventually deliver the oxygen-rich blood to the rest of the body.

As is apparent from the description above, the proper sequence ofcontraction and relaxation of the heart chambers is fundamental to itsoperation. Contraction of the heart chambers is controlled by theheart's conduction system, which includes areas of specialized "nodal"tissue or "nodes" capable of generating and transmitting electricalimpulses. The ability to generate electrical impulses is known as"automaticity."

The natural pacemaker of the heart is called the SA (sino-atrial) node.It lies in the groove where the superior vena cava joins the rightatrium. The SA node contains two types of cells, one of which exhibitsautomaticity.

In general, the conduction of an electrical impulse generated by the SAnode proceeds as follows. The cardiac impulse travels across the wallsof the atria, eventually causing the atria to contract. The impulsesgenerated by the SA node are also transmitted to the atrio-ventricular(AV) node located in the lower portion of the right atrium near theright ventricle. From the AV node, the impulses travel through anotherarea of nodal tissue known as the bundle of His and eventually to thePurkinje's fibers that envelop the ventricles. When the impulses reachthese fibers, they cause the ventricles to contract.

More specifically, from the SA node the cardiac impulse spreads radiallyalong ordinary atrial myocardial fibers. A special pathway, the anteriorinteratrial myocardial band, conducts the impulse from the SA nodedirectly to the left atrium. In addition, three tracts, the anterior,middle, and posterior internodal tracts or pathways constitute theprincipal routes for conduction of the cardiac impulse from the SA tothe AV node. These tracts consist of ordinary myocardial cells andspecialized conducting fibers.

The AV node is situated posteriorly on the right side of the muscle walldividing the heart's right and left atria, (known as the interatrialseptum). The AV node also contains cells that exhibit automaticity. TheAV node receives and relays the impulses through the septum to a clusterof fibers between the ventricles known as the bundle of His.

The bundle of His passes down the right side of the inter ventricularseptum (the muscle wall between the right and left ventricles) and thendivides into the right and left bundle branches. The right bundle branchis a direct continuation of the bundle of His and it proceeds down theright side of the interventricular septum. The left bundle branch, whichis considerably thicker than the right, branches almost perpendicularlyfrom the bundle of His and bisects the interventricular septum. On thesurface of the left side of the interventricular septum the main leftbundle branch splits into a thin anterior division and a thick posteriordivision.

The right bundle branch and the two divisions of the left bundle branchultimately subdivide into a complex network of conducting fibers calledPurkinje's fibers which envelop the ventricles.

As an impulse travels from the region of the atria to the ventricles,the first portions of the ventricles to be excited are theinterventricular septum and the papillary muscles. The wave ofactivation spreads to the septum from both its left and its rightendocardial surfaces (the inner membrane of the heart wall). Earlycontraction of the septum tends to make it more rigid and allows it toserve as an anchor point for the contraction of the remainingventricular myocardium (the middle layer of muscle that comprises theheart wall).

The endocardial surfaces of both ventricles are activated rapidly, butthe wave of excitation spreads from endocardium to the outer membrane orsheath of the heart wall known as the epicardium at a slower velocity.Because the right ventricular wall is appreciably thinner than the left,the epicardial surface of the right ventricle is activated earlier thanthat of the left ventricle. The last portions of the ventricles to beexcited are the posterior basal epicardial regions and a small zone inthe basal portion of the interventricular septum.

Cardiac arrhythmia refers to a disturbance in the rhythm of contractionand relaxation of the heart's chambers. In cardiac arrhythmia, the atriaand/or ventricles do not contract and relax in the regular andsequential pattern described above, and may instead contract prematurelyand/or randomly. In the most serious types of arrhythmia, such asfibrillation, the impulses may fragment into multiple, irregularcircuits which are incapable of causing coordinated contractions of theheart chamber and, therefore, may adversely affect the pumping of blood.

Various causes of arrhythmia have been identified. One cause of cardiacarrhythmia may be a disorder in the formation of the impulse. Forexample, although the primary source of impulse formation is the SAnode, it is known that most cardiac cells are capable of exhibitingautomaticity. If an impulse traveling, for example, from the SA node isdelayed or diverted, other cardiac cells or clusters of cells outsidethe areas of nodal tissue may spontaneously initiate an impulse. Thesecells or cell clusters are known as ectopic foci. The impulses generatedby ectopic foci may be transmitted to the atria and/or ventricles priorto the impulse that is traveling along the normal conductive pathway,thereby causing premature contraction of the heart chamber.

Arrhythmia may also be caused by disorders in the conduction ortransmission of an impulse from one region of the heart to anotherregion. In this case, injury to a section of the heart tissue that ispart of the normal conductive pathway may slow, block or even diverttransmission of the impulse from its normal path. Impulses travelingalong a different pathway proximal to the blocked pathway may attempt toreenter the blocked pathway. If the impulse reenters the blockedpathway, it may prematurely stimulate other nodal tissue causing theatria or ventricles to contract before these chambers have returned totheir relaxed state.

One known method of treating cardiac arrhythmia, includes ablating thefocal point of the arrhythmia within the heart tissue with the tip of acatheter or other surgical device. The devices used for treatingarrhythmia typically have elongated, small diameter tubular bodies thatinclude tips that can be heated, super-cooled or are capable of emittingradiofrequency energy. Typically, the device is introduced and advancedthrough the vascular system of the patient until the tip of the devicereaches the desired location (e.g. the suspected source of thearrhythmia for treatment). When applied to the source of the arrhythmia,these heated, super-cooled or otherwise energized catheter tips ablatethe section of tissue responsible for the cardiac arrhythmia.

One such method for treating disorders associated with the conduction ofelectrical signals in cardiac tissue is described in U.S. Pat. No.4,641,649. There, an antenna located at the distal tip of the catheterreceives electrical signals from the heart which aids the physician indetermining the source of the cardiac disorder. Once the source has beenlocated, radiofrequency or microwave frequency energy is applied to thesection of tissue through the tip of the catheter to ablate the sourceof the electrical disorder. The ablation can be controlled by means ofan attenuator which regulates the amount of power radiated by theantenna.

Another example of a method and apparatus for ablating a portion of bodytissue is described in U.S. Pat. No. 5,147,355. There, a catheter isguided through the patient's body to the area of tissue to be ablated.An electrode located at the catheter tip monitors electrical activity ofthe tissue and transmits the information to a monitor display. After thephysician has positioned the tip of the catheter at the suspected sourceof the arrhythmia, the tip of the catheter is cryogenically super-cooledto ablate the desired section of heart tissue. The device in this patentincludes a flow control valve to regulate the amount of cryogenic liquiddelivered to the catheter tip, and thereby try to control thetemperature and rate of tip cooling. It is unclear from the descriptionin U.S. Pat. No. 5,147,355 how or whether the operator is able todetermine the tip temperature. If during the course of cryoablation, anarrhythmic signal continues to be detected by the electrode, thecryoablation may be curtailed and the catheter tip repositioned tocryoablate another section of tissue suspected of being the source ofthe arrhythmia.

The catheter described in U.S. Pat. No. 5,147,355 includes first andsecond concentric fluid flow passages adjacent the tip portion for theflow of cryogenic fluid. Accordingly, the flow passages of the cathetermust be made of a rigid material such as stainless steel or othermaterial capable of withstanding the high pressures and temperatures aslow as -60° C. associated with liquid-to-gas phase change in a cryogenicfluid. As a result, the catheter is necessarily less flexible and moredifficult to maneuver than is desirable when advancing the catheterthrough the vascular system of a patient.

One of the drawbacks with the above-described method for treatingcardiac arrhythmia is that it does not allow for precise control of theprobe tip temperature. For example, in the cryoablation method describedin U.S. Pat. No. 5,147,355, the temperature of the catheter tip isregulated by the amount of cryogenic fluid delivered to the cathetertip. Using this method, change in the temperature of the probe tip isgradual, and rapid and precise temperature adjustment to the probe tipover a broad range of temperatures is difficult to achieve. Theinability to quickly adjust the probe tip temperature may result in somedestruction of sections of heart tissue that are not responsible for thearrhythmia.

Although it is known that cooling the heart tissue can cause observablechanges in the electrical activity of the heart, Hariman et al.,"Cryothermal Mapping of the Sinus Node in Dogs: A Simple Method ofLocalizing Dominant and Latent Pacemakers," Cardiovascular Research,1989, Vol. 23, pp. 231-238 and Gessman, "Localization and Mechanism ofVentricular Tachycardia by Ice-Mapping 1-Week After the Onset ofMyocardial Infarction in Dogs," Circulation, Vol. 68, No. 3, September1983, pp. 657-666, which are incorporated by reference herein, thepresent methods for treating arrhythmia, as described above, typicallyhave not utilized cooling of the heart tissue for purposes ofidentifying the foci of the aberrant signals, but have usedlow-temperature cooling for ablation.

SUMMARY DISCLOSURE OF THE INVENTION

The present invention is generally directed to methods and apparatus foruse in procedures related to the electrophysiology of the heart, such asidentifying or evaluating the electrical activity of the heart, ordiagnosing and/or treating conditions associated with theelectrophysiology of the heart. In accordance with one aspect of thepresent invention, the apparatus includes an elongated body havingproximal and distal end portions. One or more pairs of thermocoupleelements or "legs" are located within said distal end portion. One endof one of the thermocouple elements is conductively connected to one endof the other thermocouple element at a junction. The other end of atleast one thermocouple element is connected to a heat sink. Thetemperature of the junction may be affected by applying a voltage acrossthe thermocouple elements in accordance with the Peltier effect and bysaid heat sinks.

In accordance with another aspect of the present invention, a probe foruse in cardiac-related procedures is also provided. The probe includes acarrier having low thermal and electrical conductivity and at least twothermocouple elements conductively connected at a junction and mountedon the carrier. The probe also includes at least one electrode.

In accordance with another aspect of the present invention, a method isprovided wherein an apparatus having thermocouple elements of differentelectromotive potentials, which are conductively connected at a junctionis introduced into the interior of the heart. The junction is broughtinto contact with a section of the heart tissue. An electrical currentis passed through the thermocouple elements to reduce the temperature ofthe junction in accordance with the Peltier effect, and thereby cool theheart tissue without damaging the heart tissue. The heart is monitoredfor any effect of the cooling (by, for example, direct observation by aphysician or by sensing or recording by a machine). After cooling, thetemperature of the heart tissue is returned to normal, such as byactually warming the heart tissue or by allowing the heart tissue towarm on its own.

Finally, in accordance with another aspect of the present invention, amethod for treating electrophysiological disorders in the heart is alsoprovided. As in the method referred to above, an apparatus havingthermocouple elements of different electromotive potentials conductivelyconnected at a junction is introduced into the interior of the heart,and a section of heart tissue is contacted with the junction. Thejunction is cooled by passing an electrical current through thethermocouple elements in accordance with the Peltier effect, and therebycool the heart tissue without damaging the heart tissue. The heart maybe monitored for an effect of such cooling. By monitoring for the effectof the cooling on the electrophysiology of the heart, the physician isable to determine whether or not the source of the arrhythmia has beenlocated. If it is determined that the source of the arrhythmia has beencorrectly identified, the section of tissue may be immediately treated,for example, by ablating the desired area while the junction is still incontact with the section of heart tissue, so as to substantiallypermanently interrupt the source of the arrhythmia. During ablationelectrical current is passed through the thermocouple elements inaccordance with the Peltier effect.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a human heart with the apparatusembodying the present invention disposed within the heart at differentlocations;

FIG. 2 is a longitudinal cross-sectional view of the distal end portionof an apparatus utilizing the Peltier effect;

FIG. 3 is a plan view of the apparatus embodying the present invention;

FIG. 4 is a longitudinal cross-sectional view of the distal end of theapparatus of FIG. 3;

FIG. 5 is a transverse cross-sectional view taken through 5--5 of thedistal end of FIG. 4;

FIG. 6 is a more detailed elevational view of the distal end of theapparatus of FIG. 3;

FIG. 7 is a plan view of another embodiment embodying the apparatus ofthe present invention;

FIG. 8 is a longitudinal cross-sectional view of the distal end of theapparatus FIG. 7;

FIG. 9 is a transverse cross-sectional view taken through 9--9 of thedistal end of FIG. 8;

FIG. 10 is a more detailed elevational view of the distal end of theapparatus of FIG. 7;

FIG. 11 is a longitudinal cross-sectional view of another embodiment ofthe distal end of an apparatus embodying the present invention;

FIG. 12 is a transverse cross-sectional view taken through 11--11 of theapparatus of FIG. 11;

FIG. 13 is a transverse cross-sectional view of another embodiment ofthe distal end of an apparatus embodying the present invention;

FIG. 14 is longitudinal cross-sectional view of another embodimentembodying the present invention.

FIG. 15 is a plan view of an embodiment of a thermocouple carrier thatmay be used in the present invention;

FIG. 16 is a longitudinal cross-sectional view of an alternativeembodiment of a thermocouple carrier that may be used in the presentinvention;

FIG. 17 is a transverse cross-sectional view, taken through 17--17 ofthe thermocouple carrier of FIG. 16;

FIG. 18 is a plan view of another embodiment of the apparatus embodyingthe present invention;

FIG. 19 is a longitudinal cross-sectional view of the apparatus of FIG.18;

FIG. 20 is a cross-sectional view of the apparatus of FIG. 18 takenalong 20--20;

FIG. 21 is a cross-sectional view of the apparatus of FIG. 19 takenalong 21--21;

FIG. 22 is a plan view of the distal tip of the apparatus embodying thepresent invention with a distal end cap;

FIG. 23 is a longitudinal cross-sectional view of the distal tip of FIG.22;

FIG. 24 is a cross-sectional view of the distal tip of FIG. 23 takenalong 24--24;

FIG. 25 is a plan view of an alt ernative distal tip of the apparatusembodying the present invention;

FIG. 26 is a longitudinal cross-sectional view of the tip of FIG. 25;

FIG. 27 is a cross-sectional view of the tip in FIG. 26 taken along27--27;

FIG. 28 is a cross-sectional view of an alternative embodiment of theapparatus embodying the present invention;

FIG. 29 is a cross-sectional view of another alternative embodiment ofthe apparatus embodying the present invention;

FIG. 30 is a cross-sectional view of another alternative embodiment ofthe apparatus embodying the present invention; and

FIG. 31 is a cross-sectional view of another alternative embodiment ofthe apparatus embodying the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the drawings, FIG. 1 shows a distal end portion of anelongated catheter 10, as it may be used in accordance with the presentinvention, disposed within a human heart 12. More particularly, thedistal end portion includes a catheter probe 14 in contact with aselected area of heart tissue. Herein, the term "probe" refers to anapparatus located at the distal end portion of the catheter thatincludes the thermocouple elements of different electromotive potential,as described in more detail below. As used herein, the term "catheter"is intended to refer to the entire catheter apparatus from proximal todistal ends, and including the "probe."

The probe 14 employed in the catheter 10 incorporates a thermocouplegenerally of the type described in U.S. Pat. No. 4,860,744. As set forthin that patent, such thermocouples may comprise two elements or "legs"of differing materials having a large difference in electromotivepotential (i.e., different Seebeck coefficients). The difference inelectromotive potential between the two elements or "legs" is achievedby doping the elements to produce either positive (P-type) or negative(N-type) elements. The two elements are conductively joined at one endto form a junction. When current flows through the elements, one end ofeach thermocouple element is cooled while the other end of eachthermocouple element is heated. The direction of the current determineswhich end is cooled and which is heated. This phenomenon is known as thePeltier effect. A detailed description of the Peltier effect and a probe14 (shown in FIG. 2) utilizing the Peltier effect is set forth in U.S.Pat. No. 4,860,744 titled "Thermoelectrically Controlled Heat MedicalCatheter" which is incorporated by reference herein.

As described in U.S. Pat. No. 4,860,744 and generally shown in FIG. 2 ofthe present application, probe 14 utilizes a single thermocouple designsometimes referred to as a unicouple. The unicouple utilizes one pair ofP and N thermocouple elements or legs. The P leg 16 and N leg 18 areelectrically separated along their lengths, but are conductively joinedat one end. These ends of the thermocouple are referred to as junctions24, 24'. The P and N legs 16, 18 are separately connected to connectorwires 20, 20' through which electrical current is fed. In general,thermoelectric heating of junctions 24, 24' occurs when an electricalcurrent is passed through the couple in the P to N direction. When thedirection of the current is reversed, by reversing the voltage, the tipof probe 14 is cooled in accordance with the above-described Peltiereffect.

It should be noted that the above-identified patent is particularlydirected to the use of the Peltier effect for heating a probe tip tomelt or vaporize deposits in a patient's body such as atheromatousplaque--an application very different from that claimed herein.

One embodiment of the apparatus of the present invention is shown inFIG. 3. More particularly, FIG. 3 shows a catheter 40 forcardiac-related procedures such as identifying or evaluating theelectrical activity of the heart (by, for example, mapping), identifyingan electrophysiological source of heart arrhythmia and/or treating heartarrhythmia.

Catheter 40 comprises an elongated hollow tube constructed of anysuitable, biocompatible material. The material used for the cathetershould be flexible so that the catheter may be easily guided through thevascular system of the patient. An example of such a material ispolyurethane. Braiding or other stiffening material may be used inaccordance with known techniques, as desired, to allow improved controlof the catheter or to permit insertion of the catheter without the useof a guiding device.

As shown in FIG. 3, catheter 40 includes a proximal end portion 42 and adistal end portion 43. Distal end portion 43 of catheter 40 includes aprobe portion or "probe" 44 for contacting the heart tissue. To assistin the positioning of the probe 44 within the interior of the heart, asteering wire 46 may be provided, which extends through the catheter 40essentially between distal end portion 43 (at or near the probe) and aslidable hub 48 located near or within the proximal portion 42. As seenin FIG. 3, sliding hub 48 causes the distal end portion 43 (and theprobe 44) of catheter 40 to bend. This may assist in guiding the probeto the desired location and bringing the probe 44 into contact with thesurface of the heart tissue. Once the probe 44 has been positioned at ornear the desired location of the heart tissue, the electrical activityof the heart may be identified, evaluated or mapped, andelectrophysiological sources of arrhythmia may be identified and/ortreated.

As shown in FIGS. 4 and 6, probe 44 includes a thermocouple carrier 47,for retaining and supporting the heating and cooling elements describedbelow. In general, thermocouple carrier comprises a molded body,approximately 10mm in length, for supporting thermocouple elements or"legs" 48 and 50. The thermocouple carrier should be made of a rigidmaterial that is relatively easy to machine and/or mold. Furthermore,the material used for the thermocouple carrier should have low thermalconductivity and low electrical conductivity. One such suitable materialis a polyether ether ketone (PEEK).

The thermocouple carrier 47 of FIGS. 4 and 6 is shown withoutthermocouple elements 48 and 50 in FIGS. 16 and 17. As seen in FIG. 16,thermocouple carrier 47 is generally cylindrical and includes distalbore 47a, proximal bore 47b and recessed area 49 between the bores forreceiving thermocouple elements 48 and 50. A groove 51 below recessedarea 49 forms an off-center passageway, which provides a conduit for thedifferent wires and sensors used in the probe. (These wires and sensorsare described in more detail below.) Wall portion 53 separates andinsulates groove 51 (and the wires that typically extend therethrough)from recessed area 49 (and the thermocouple elements typically disposedtherein). An opening 53a in wall portion provides a conduit (for atemperature sensor described below) between recessed area 49 and groove51. The location of the wires within the thermocouple carrier 47relative to the thermocouple elements is more clearly seen in FIG. 4.

As shown in FIG. 4, thermocouple elements or legs 48 and 50 arepositioned within thermocouple carrier 47 in a longitudinally extendingend-to-end arrangement (i.e. the thermocouple element 50 beingpositioned in a more distal location relative to the other thermocoupleelement 48). Both of the thermocouple elements 48 and 50 are connectedat their ends to a power supply (as generally shown in FIG. 1) viaconnecting wires 52 and 54 for applying a voltage and inducing currentthrough the thermocouple elements 48 and 50. Typically, connecting wires52 and 54 are soldered to the thermocouple elements 48 and 50, althoughother attachment means also may be used. The other ends of thermocoupleelements 48 and 50 are joined to form a junction 56 which may be cooledor heated depending on the direction of the current and in accordancewith the above-described Peltier effect. As shown in FIGS. 4 and 6, inthe preferred embodiment, junction 56 is spaced from the very tip ofprobe 44. Placement of junction 56 at a location spaced from the probetip (i.e., on the "side" of probe 44) makes it easier to position andmaintain the probe in contact with the pulsating heart.

Thermoelectric cooling of the junction 56, occurs when an electricalcurrent is passed from a power supply through wires 52 and 54 tothermocouple elements 48 and 50. When the direction of the current isreversed by reversing the voltage in the power supply, the junction 56is heated. Thus, by controlling the voltage of the power supply and thecurrent through thermocouple elements, one can effectively and quicklycontrol and adjust the temperature of junction 56.

As cooling or heating of junction 56 is achieved by introducing acurrent through the thermocouple elements 48 and 50 in a specificdirection, it is desirable that the thermocouple elements be made of amaterial that can be quickly and efficiently cooled and/or heated.Although several different materials may be used, preferably thethermocouple elements are made of alloys including Bismuth-Telluride(Bi-Te). The thermocouple elements may include other materials or beappropriately doped (as described in U.S. Pat. No. 4,860,744) to producea P-type element and an N-type element. For example, in the presentinvention, the p-type element may include 72% Antimony Telluride (Sb₂Te₃), 25% Bismuth Telluride (Bi₂ Te₃) and 3% Antimony Selenide (Sb₂ Se₃)doped with excess Tellurium (Te). The n-type element may include 90%(Bi₂ Te₃), 5% (Sb₂ Se₃) and 5% (Sb₂ Te₃) doped with Antimony Triodide(Sb I₃).

The wires that connect the thermocouple elements 48 and 50 to the powersupply should be flexible, having a low electrical resistance and alarge surface area for heat transport such as, for example, a Litz wireavailable from Kerrigan Lewis Manufacturing Co. of Chicago, Ill. (partor product no. 210/48). Junction 56 is preferably formed by solderingthe ends of thermocouple elements 48 and 50 with an organicbiocompatible solder that has a high melting point, high thermalconductivity and has a high degree of electrical conductivity. Anexample of such an organic solder is part or product no. 5N60PB4066available from Kester Solder Co. of Des Plaines, Ill.

Gaps between the ends of elements 48 and 50 and the carrier arepreferably filled with a thermally conductive epoxy 57. The epoxy 57 maybe finished to provide a smooth exterior surface for the probe. Theepoxy also assists in drawing heat from the hot ends of the thermocoupleelements, thereby assisting in maintaining the cool ends of thethermocouple elements at the desired temperature. One such epoxybelieved to be suitable is Oxy Cast made by Resin Technology of Easton,Mass.

Precise temperature control of the junction 56 may be achieved byprecalibration of the power supply so that the temperature achieved by agiven current flow is accurately known. Alternatively, the temperatureof the junction 56 may be actually monitored. Various devices formonitoring the temperature of junction 56 may be used without departingfrom the present invention. In the illustrated embodiment thetemperature of junction 56 may be measured and monitored by atemperature sensor 58 which is embedded in the solder junction 56.Temperature sensor 58 extends from junction 56, through opening 53a,groove 51 and proximal bore 47b of thermocouple carrier 47, through thebody of catheter 40 and is attached to a standard temperature monitoringdisplay (not shown). In this embodiment, the temperature sensor 58 maybe made of an iron/constantan material that is teflon insulated and hasa diameter of about 1.1 mm (0.005 inches). The length of temperaturesensor will naturally depend on the length of the probe and catheter.Such a sensor is available from OMEGA Engineering of Stanford, Conn. andsold as product or part no. 5SC-TT-J-36-72. Alternatively, athermocouple thermometer may be used to monitor the temperature of thejunction. Still other means for monitoring the temperature of the probe40 are set forth in U.S. Pat. No. 4,860,744, and in U.S. Pat. No.5,122,137, assigned to Boston Scientific and also incorporated byreference.

In addition, as shown in FIGS. 4 and 6, probe 44 also includes spacedelectrodes 62 and 64 for monitoring the electrical signals in the hearttissue. By monitoring the electrical signals in the heart, theelectrodes assist in identifying the location of the heart arrhythmia ordamaged heart tissue. The distal electrode 62, shown in FIGS. 4 and 5,is located at the tip of the probe 44. Distal electrode may be made ofstainless steel (such as SS316) or any other suitable electricallyconductive and biocompatible material. Proximal electrode 64, shown inFIGS. 4 and 6, is approximately 1.5 mm in length and is also made of anelectrically conductive and biocompatible material. Distal and proximalelectrodes 62 and 64 are preferably spaced equal distances from junction56.

As shown in FIG. 4, distal electrode 62 is connected to a monitoringdevice 37 (as generally depicted in FIG. 1) such as an ECG by wire 65which is soldered or otherwise connected to the distal electrode 62 andextends through passageway 49 of thermocouple carrier 47. Proximalelectrode 64 is also connected by a soldered wire (not shown) to amonitoring device 37. The wires that connect the distal and proximalelectrodes to the monitoring device 37 should be of a flexible materialhaving a small diameter and a low electrical resistance. A wire believedto be suitable in this and the other embodiments described herein is acopper wire, 36 AWG with polyamide insulation, available from Mid-WestWire Specialties Co. of Chicago, Ill.

Turning now to FIG. 7, another embodiment of the apparatus of thepresent invention is shown. In particular, FIG. 7 shows an apparatussuch as catheter 66 which may be used for cardiac-related proceduressuch as evaluating (by, for example, mapping) the electrical activity ofthe heart, identifying the source of heart arrhythmia and/or treatingheart arrhythmia. Catheter 66 has a hollow body portion and is made of asuitable, flexible, biocompatible material such as polyurethane. As seenin FIG. 7, catheter 66 includes a proximal portion 67 and a distal endportion 68. Distal end portion 68 includes a probe portion or "probe" 69for contacting the heart tissue. Directional control of the probe may beachieved by steering wire 70 in the manner previously described.

A general view of the probe 69 is seen in FIG. 10 and a more detailedcross-sectional view of probe 69 is shown in FIG. 8. As seen in FIG. 8,thermocouple elements or legs 72 and 74 are arranged on thermocouplecarrier 76 in a parallel or "side-by-side" arrangement. A more detailedview of thermocouple carrier 76 is shown in FIG. 15. As seen in FIG. 15,thermocouple carrier 76 includes a hollow body portion 76a and two thin,elongated, spaced apart support members 76b and 76c extending betweenand supporting the thermocouple elements 72 and 74 in a spaced apartrelationship. Referring back to FIG. 8, wires 78 and 80 are connected(as by soldering) to the proximal ends of thermocouple elements 72 and74 and extend through the hollow body portion 76a of thermocouplecarrier 76 and through the body of the probe 69 and catheter 66 (as seenin FIG. 8) to a power supply (shown generally in FIG. 1). The distalends of thermocouple elements 72 and 74 are soldered to distal electrode82 to form a "junction" between the elements of the thermocouple. Inthis manner, distal electrode/junction 82 may be cooled or heated byapplying a voltage across the thermocouple elements 72 and 74 to inducean electrical current through thermocouple elements 72 and 74.

As described above in connection with the earlier embodiment,thermocouple elements 72 and 74 should be made of a material that can bequickly and efficiently cooled (e.g. Bi-Te). In addition, thermocoupleelements may include other materials or be appropriately doped toprovide a P-type element and an N-type element as discussed above inconnection with the embodiment of FIGS. 3-6. Wires 78 and 80 should beflexible, have a low electrical resistance and a large surface area forheat transport such as, for example, the above-described Litz wire.

A thermoconductive epoxy 83 of the type described above may be used tofill the gaps between the proximal ends of the thermocouple elements 72,74 and body portion 76a of thermocouple carrier to form a smoothcontinuous outer surface of probe 69. In addition, epoxy 83 draws heatfrom the ends of the thermocouple elements and, thereby, assists inkeeping the other ends of elements 72 and 74 cool.

Referring still to FIG. 8, a temperature sensor 84 extends through thebody of catheter 66 and through probe 69 between thermocouple elements72 and 74, where it is preferably embedded in the solder used toconductively connect the thermocouple elements 72 and 74 to the distalelectrode 82.

In addition to distal electrode/junction 82, probe 69 also includes aproximal electrode 86. Like distal electrode 82, the proximal electrodeassists in locating the diseased heart tissue. The proximal electrodecan also serve as a backup for the distal electrode/junction 82 if, forexample, the electrode function of the distal electrode/junction 82 isadversely affected by the conductivity of the attached thermocoupleelements. Finally, proximal electrode 86 may be used to ground thesystem.

Distal electrode/junction 82 and proximal electrode 86 are connected toa monitor, such as an ECG, (shown in FIG. 1) which records theamplitudes of the electrical signals detected by the electrodes 82 and86. More specifically, proximal electrode 86 is connected to the monitorvia wire 88. Distal electrode/junction 82 transmits electrical signalsthrough wires 78 and/or 80 to the monitor via a switching device (notshown) for establishing an electrical connection between wires 78 and/or80 and the monitoring device. Alternatively, wires 78 and/or 80 may bedetached from the power supply and connected to the monitoring device.As in the earlier embodiment, electrodes 82 and 86 should be of anelectrically conductive and biocompatible material. In the presentembodiment, for example, distal electrode 82 comprises a silver cap.Wire 88 should be flexible, have a small diameter and have a lowresistance.

Still another embodiment of the present invention and, in particular of,a probe is shown in FIGS. 11-12. As seen, for example, in FIG. 11, probe90 includes two sets of thermocouple elements and utilizes a "two stagecooling process." More specifically, probe 90 includes a primary set oftwo thermocouple elements 92 and 94 (i.e. located near the distal tip ofprobe 90) and a secondary set of two thermocouple elements 96 and 98spaced from elements 92 and 94. Both sets of thermocouple elements aresupported by thermocouple carrier 100 similar to the thermocouplecarrier shown in FIG. 8. The thermocouple elements are made of the samematerial as the elements described above and/or may be doped orotherwise combined with other materials to provide P-type and N-typeelements.

A thermoconductive epoxy 102 may be used to fill the gaps between theprimary and secondary sets of thermocouple elements and the thermocoupleelements and carrier 100. As described above in connection with theother embodiments, epoxy 102 also draws heat from the proximal ends ofthermocouple elements 92 and 94 to allow for greater cooling capacity atprobe tip. As in the above-described embodiments, the thermocoupleelements are connected to a power supply (not shown) via wires 104, 106,108 and 110 for introducing electrical current to the thermocoupleelements. Wires 104, 106, 108 and 110 are preferably Litz wires of thetype described above, but can also be any flexible wire having a lowelectrical resistance and a large surface area for heat transport. Probe90 also includes a distal electrode (and junction) 112 and a proximalelectrode (not shown). As described above the electrodes are connectedto a monitor which records the amplitudes of the electrical signals ofthe heart tissue.

Cooling of the probe 90 occurs at the distal electrode/junction 112which is electrically connected (soldered) to thermocouple elements 92and 94. The secondary set of thermocouple elements 96 and 98 are alsoconductively connected to form junction 112a. When cooling of the probeis desired, the distal ends of thermocouple elements 92, 94, 96 and 98and more specifically, junctions 112 and 112a are cooled while theproximal ends of legs 92 and 94 and legs 96 and 98 are heated. Becausesome heat transfer from the proximal ends of legs 92 and 94 to thedistal ends of legs 92 and 94 may occur, complete cooling of distalelectrode/junction 112 may not be attained. Accordingly, the cooledjunction 112a of the second set extracts heat from the proximal ends ofthe first set to provide greater cooling capacity at the distal ends oflegs 92 and 94. Alternatively, and by the same principle, if the currentis reversed, greater heat capacity can be obtained at the distal ends oflegs 92 and 94, and, in particular, distal electrode/junction 112. Atemperature sensor 114 of the type described above may also be used tomonitor the temperature of distal electrode/junction 112. One end oftemperature sensor is embedded in the solder used to connectthermocouple elements 92 and 94 to distal electrode/junction 112 and theother end to a temperature monitoring device.

FIG. 13 shows a cross-sectional view of another variant of the two-stagecooling probe similar to the embodiment shown in FIGS. 11-12. In theembodiment of FIG. 13, the primary (distal) thermocouple comprises twothermocouple elements as described above. As seen in FIG. 13 which is atransverse cross-sectional view taken through the secondary set ofthermocouple elements, the secondary (proximal) thermocouples comprisetwo sets of two thermocouple elements 113 a,b, c and d. Typically, thesethermocouple elements are smaller in size than the thermocouples in theprimary set. Element 113a is joined to element 113d at one junction (toform one thermocouple) and elements 113b and 113c are joined at a secondjunction (to form a second thermocouple). In all other respects, theprobe of FIG. 13 is analogous to probe 90 of FIGS. 11-12.

Finally, another embodiment of the present invention and, in particular,of a probe, is shown in FIG. 14. This particular embodiment, isessentially the same as described in connection with FIG. 4, except thata heatable tip is provided for use in ablating or treating heart tissue.For example, in FIG. 14, thermocouple elements 116 and 118 are arrangedin an end-to-end arrangement within thermocouple carrier 120 withjunction 122 formed between thermocouple elements 116 and 118. Elements116 and 118 are connected, via wires 118b and 118a, to a power supply(shown generally in FIG. 1) for applying a voltage across thethermocouple elements and introducing a current through elements 116 and118 to cool junction 122. The temperature of junction 122 is monitoredby temperature sensor 124. If it is desired to ablate tissue by heating,however, the tip 126 of the probe is heated. As shown in FIG. 14, wire128 for introducing radio frequency or other ablation energy extendsfrom a power supply to the distal tip 126. In all other respects, thematerials used are similar to the materials and method set forth above.

Turning now to the methods of using the foregoing apparatus in carryingout procedures related to the electrophysiology of the heart, such asevaluating (by mapping) the electrical activity of the heart,identifying the electrophysiological source of cardiac arrhythmia andtreating the arrhythmia, the catheter (10, 40, 66) is introduced into apatient percutaneously and advanced into proximity with the desiredsection of the heart 12 (FIG. 1). The present invention is not limitedto the means by which the catheter is advanced through the vascularsystem of the patient. For example, the catheter may be advanced througha guiding or positioning catheter or sheath, or over a guide wire. Forin-the-heart procedures a guiding or positioning catheter may bepreferred over a guide wire. In addition to known apparatus andtechniques for advancing the catheter through the vascular system ofpatients, a novel positioning catheter such as the one described in U.S.Ser. No. 08/197,122 filed on Feb. 16, 1994 and assigned to the assigneeof the present application may also be used.

As described in more detail below, after the catheter has beensufficiently advanced into the vascular system of the patient, the probe(14, 44, 69, 90) is introduced into the heart interior and brought intocontact with the desired section of the heart tissue as generally shownin FIG. 1. More specifically, the junction (24, 56, 82, 112, 122) of theprobe is brought into contact with the desired section of tissue. Anelectrical current is then passed through the thermocouple elements toreduce the temperature of the junction (in accordance with the Peltiereffect) and thereby cool the contacted heart tissue. The effect of thecooling on the heart and specifically the effect on the electricalactivity of the heart, if any, may be monitored.

The desired section of heart tissue contacted by the probe may bepre-selected by the physician or may be determined based on the presenceor absence of electrical activity at that section as detected by theelectrodes (62, 64, 82, 86) on the probe and displayed on the ECG 37 orother device.

In accordance with a further aspect of the present invention, thelocation of the electrical activity in the desired section may beaccurately determined.

For example, in the embodiment of FIGS. 3-6, the junction 56 is midwaybetween the electrodes 62 and 64. If the amplitudes of the signalsreceived and transmitted by electrodes 62 and 64 are not substantiallyequal, this is an indication the sensed electrical activity is notlocated between the two electrodes. In that case, the probe may berepositioned until the signals are of approximately equal amplitude.Equal amplitudes for the signals being received by the proximal anddistal electrodes 64, 62 indicates (to the physician) that the desiredsection of tissue is located at equal distances between the twoelectrodes 62 and 64 and, ideally, opposite the location of junction 56(which, as described above, is also located at equal distances betweenelectrodes 62 and 64). If desired, additional electrodes may also beused to monitor the electrical activity of the heart.

After the junction is placed at the desired section of heart tissue,cooling is achieved by establishing a voltage across the thermocoupleelements so as to cause a flow of electric current through thethermocouple elements in order to cool the junction. The temperature ofthe junction is determined by the directional flow of current (P to N orN to P) as described in U.S. Pat. No. 4,860,744 which has beenincorporated by reference. With the junction in contact with the hearttissue, the effect of such cooling on the electrophysiology of theheart, can be observed on the monitoring device 37 (FIG.1) connected toelectrodes.

In the present invention, the junction preferably is cooled to atemperature necessary to affect the electrical activity of the heart atthe particular section of tissue without permanently damaging the hearttissue. It is preferred, however, that the junction be cooled to atemperature between approximately -50° C. and 37° C., although anycooling below 27° C. is generally adequate to affect the rate ofconduction. For example, the probe may be cooled to betweenapproximately -15°--32° C. In fact, it has been shown that cooling theheart tissue by at least 10° C. can be sufficient to affect and/orsuppress the electrical activity of the heart tissue. Whatever thetemperature of the probe junction, it is desirable that the temperatureof the contacted heart tissue not be lowered below 6° C. and bemaintained between approximately 6°-27° C. or 10°-20° C.

Once the junction has been cooled to its desired temperature, contactbetween the junction and the heart tissue is maintained for, in general,between about 1 second and 15 minutes, depending on the temperature ofthe junction and the likely depth of the source of the electricalactivity within the heart tissue. Electrophysiological changes will alsodepend on where in the heart the signal is monitored. The contact timewill generally be less when the probe and, more specifically, thejunction is particularly cold, for example, 20° C. or less and/or whenthe suspected electrical focus is at a shallow depth within the hearttissue. On the other hand, when the junction is not cooled below about27° C., the contact time may require several minutes to affect theelectrical signal foci that are at a significant depth within thetissue. In either case, the junction is preferably cooled only to theextent necessary to affect the electrical activity without resulting inpermanent damage to the heart tissue. A significant benefit of thepresent invention is that it allows the physician precise and immediatecontrol over the temperature of the probe tip, thereby reducing the riskof unnecessary damage to the heart tissue.

The particular steps which follow the steps described above will vary,depending on the objective of the procedure. If the objective of theprocedure is to identify or "map" the electrical activity of the heart,then the probe may be repositioned at different locations of the heartand the above steps of contacting a section of heart tissue with thejunction of the probe and cooling the junction and monitoring arerepeated.

If the objective of the procedure is to identify theelectrophysiological source of heart arrhythmia, the above steps mayalso be carried out until the source of the arrhythmia is located. Ifupon cooling of the junction, it is determined that theelectrophysiological source of arrhythmia has not been located, theheart tissue may be returned to its normal temperature by terminatingthe flow of current and allowing the tissue to warm on its own or, forexample, by reversing the current (in accordance with the Peltiereffect) and warming the heart tissue with the probe. The probe may thenbe repositioned and the steps of contacting and cooling repeated at thenew location.

If the source of the arrhythmia is located and the objective of theprocedure is to treat the heart arrhythmia, then the probe may befurther cooled or otherwise energized or heated (at, for example, thejunction 24, 56, 82, 112 or the tip 126 in FIG. 14). More specifically,the probe is further cooled, energized or heated to treat or ablate thesection of heart tissue believed to be the source of the arrhythmia soas to permanently interrupt the aberrant electrical signal.

The precise temperature control provided by the apparatus describedabove is particularly advantageous in diagnosing and treatingarrhythmia. For example, if during cooling of the junction, it isdetermined that the arrhythmic signal has not been located, cooling ofthe junction may be quickly terminated by, for example, terminating theflow of current or reversing the flow of current so as to heat thejunction. On the other hand, if it is determined that the arrhythmicsignal has, in fact, been located, the probe (and specifically thejunction) may be immediately energized by, preferably, radio frequency(RF) energy. The radio frequency energy may be introduced from the samepower supply used to introduce the Peltier heating but modified to alsogenerate RF waves. Alternatively, a separate power supply forspecifically generating the RF waves may be used. Regardless of thesource, RF waves are transmitted through wires (e.g. 52 and 54 in FIG. 4which may be connected to a different power supply) to the thermocoupleelements to ablate the contacted tissue. Alternatively, further Peltiercooling or heating, electrical heating, or microwave energy may be usedto ablate or otherwise treat the section of tissue at the source of thearrhythmia. For effective ablation, it is preferred that the energizedjunction (or tip 126 of FIG. 14) be kept in contact with the hearttissue for between about 1 second and 15 minutes to permanently effecttreatment.

As set forth above, the present invention includes alternativeembodiments wherein the Peltier effect is used to cool the probejunction and energy such as radio frequency (RF) waves or microwaveenergy may be applied to the junction from a separate energy source forablation. In these embodiments, application of current in accordancewith the Peltier effect cools the probe junction and allows the probe tobe used for "mapping" the electrophysiology of the heart in the mannerdescribed above. During ablation (by supplying energy to the junctionfrom a separate energy source), application of current in accordancewith the Peltier effect may be continued so as to cool the junction or,more specifically, assist in controlling the temperature of the junctionduring ablation. Such embodiments are discussed in more detail below. Indiscussing these embodiments, it should be understood that unlessindicated otherwise, the components, materials, dimensions and methodsof operation of the catheter and probe are the same or similar tocomponents, materials, dimensions and methods of operation describedabove.

One such embodiment is shown in FIGS. 18-21. As shown in detail in FIG.19, probe 200 includes a carrier 202 attached to the polyurethane body204 of the catheter. Thermocouple (Peltier) elements 206 and 208 aresoldered together to form junction 210 at the distal tip of the probe.The proximal ends of thermocouple elements 206 and 208 are electricallyand thermally conductively connected, as by soldering, to heat sinks212. Heat sinks are connected to wires 214 at their proximal ends. Wires214 are in turn connected to a power supply (not shown) for introducingcurrent to the probe in accordance with the Peltier effect.

Junction 210 is separately connected to an energy source such as a radiofrequency ("RF") energy generator or microwave energy source via wire(s)216. Also, junction 210 may be connected to a temperature sensor 218which extends through probe 200 and catheter body 204 to a monitoringdevice for monitoring the temperature of the junction 210. (As in allembodiments of the present application, it is preferred that the variousconnecting wires be insulated to contain the electrical current andreduce the amount of heat generated in the vicinity of the thermocoupleelements (which may compromise the cooling ability of the elements).

As in the earlier described embodiments, a thermally conductive epoxy224 can be used to fill in the gaps within the carrier 202. Also, any ofthe embodiments described herein may include a electrically insulativepolymer jacket or coating (not shown) to cover the probe. The polymerjacket insulates the components within the probe, protects the patientfrom exposure to solders that may contain heavy metals or are otherwisenot biocompatible and assists in keeping the components of the probe inplace. The polymer jacket may be a thin layer of polyester heat shrinktubing or a thin coating of another electrically insulating polymeric orother material such as epoxy.

Electrodes in the form of pole rings 220 and 221 are spaced along probe200 for monitoring the electrical activity of the heart. Each pole ring220 is connected to a separate wire 222 which is connected to the polering through an opening 223 adjacent to pole ring in the carrier and anopening in the polymer jacket. Wire(s) 222 extends through the probe andcatheter body to an ECG device which is used to monitor, display andrecord the activity of the heart. As shown in FIG. 19, the pole ringsmay be disposed on the outer surface of the probe (220) or may bedisposed within a recessed annular groove in the probe and/or catheterbody (221). If the pole rings 220 and/or 221 are located within arecessed annular groove, it is preferred that the pole rings not berecessed within the thermocouple elements 206 and 208. Cutting into thethermocouple elements to, for example, provide the annular groove forthe pole rings reduces the surface area of the elements 206 and 208, maycause the current to find alternate paths to bypass the gap created bythe annular groove which may provide less efficient cooling. Also, itshould be understood that pole rings 220 and/or 221 are exposed forcontacting heart tissue and are not encased by the polymer jacket 226.Proximal pole ring 221 may be used to ground the system.

Preferably, probe 200 includes at least 3 electrodes (pole rings 220 and221 and junction 210), although probe 200 may include as many electrodesas necessary and as can be accommodated by the probe. Additional polerings or electrodes may be placed in other locations at or near thedistal end portion of the catheter body. The pole rings areapproximately 1.5 mm long and are spaced approximately 2 to 5 or 2 to 10mm apart. The pole rings or electrodes 220 and/or 221 may be made of anybiocompatible material that can conduct the electrical signals withinthe heart. However, it is preferred that the electrodes or pole rings bemade of either stainless steel or platinum iridium. The pole rings orelectrodes described above may be used in any of the embodimentsdescribed herein.

Like the secondary thermocouple elements shown, for example, in FIG. 11,heat sinks 212 extract heat from the thermocouple elements connected tojunction 210. The heat sinks may be any size suitable for extractingheat from the thermocouple elements. However, it has been found thatmore effective and efficient extraction of heat is achieved when theheat sinks 212 are at least as large as the thermocouple elements. Thewidth and thickness of heat sinks 212 should be the same as the widthand thickness of thermocouple elements so that the heat from thethermocouple elements is efficiently extracted from the thermocoupleelements. Additionally, a uniform width for the thermocouple elementsand heat sinks creates a uniform catheter diameter. The heat sinks maybe of any suitable length, although for more efficient heat extraction,the heat sinks should typically be as long or longer than thethermocouple elements to which they are attached or connected.

For example, where the thermocouple elements are four millimeters inlength, it is preferred that the heat sinks be approximately eightmillimeters (or approximately twice as long), as the thermocoupleelements. However, the length of the thermocouple elements should not beso long as to compromise the flexibility of the probe and distal endportion of the catheter. Accordingly, it is preferred that the length ofthe heat sinks be as long as necessary to efficiently extract heat fromthe Peltier elements without reducing the flexibility of the distalprobe. The heat sinks 212 should be of a high thermally and electricallyconductive material such as silver or gold.

By extracting heat from the thermocouple elements and, as a result,keeping the junction sufficiently cool during mapping, the heat sinksdescribed above enhance the cooling provided by the thermocoupleelements in a way that was previously unattainable using onlythermocouple elements alone. In fact, it has been discovered that byconnecting heat sinks to the thermocouple elements, the temperature atthe junction along the distal tip of the probe can be further decreased(i.e. in addition to the cooling provided by the thermocouple elements)by approximately an additional 12-20° C.

In accordance with the present invention, the distal tip of the probemay be modified to provide additional surface area for contacting theheart tissue. The additional surface area allows for easier reading ofthe electrical signals generated within the heart tissue during mappingand allows for a greater area of the tissue to be treated duringablation. Providing a greater surface area for contact with the tissuemeans that precise placement of the probe tip relative to the tissue isless critical. For example, as shown in FIGS. 22-24, the probe 200 and,more specifically, the distal tip of the probe may include a cap 230that covers the junction 210 (when the junction is located at the distalend or distal tip) and extends over a portion of the thermocoupleelements 206 and 208. Cap 230 may be made of any thermally andelectrically conductive material such as silver and may be soldered tothe distal tip of the probe.

Alternatively, the distal tip of the probe may be angled to provide forgreater surface area (for the reasons described above) at the distal endportion. As shown in FIGS. 25-27, the thermocouple elements are angledand a soldered junction 210 is formed across the angled tip. Thesoldered junction 210 may be bulbous or rounded as shown in FIG. 25, orsubstantially flat.

Another alternative embodiment of the probe is shown in FIGS. 28-29. Asin the embodiments shown in FIGS. 4 and 14, the junction 210 is locatedalong the "side" of the probe 200. As described in connection with FIG.4, placement of the junction on the "side" of the probe (as shown inFIGS. 28-31) makes it easier to position and maintain the probe incontact with the pulsating heart. Junction 210 is formed by solderingthe ends of thermocouple elements 206 and 208. The other ends ofthermocouple elements 206 and 208 are conductively connected to heatsinks 212. Heat sinks 212 are connected via wires 214 to an energysource that provides Peltier current. The thermocouple elements 206 and208, junction 210 and heat sinks 212 are contained within the carrier202 which is used to attach the probe to the catheter body 204. Athermoconductive epoxy 224 is attached to the catheter body 204. Athermoconductive epoxy 224 may be used to fill in gaps 20 between thecarrier and other parts of the probe 200.

In FIG. 29, junction 210 is connected to a temperature sensor wire 218(for measuring the temperature of the junction) and wire 216 which isconnected to a separate energy source to provide RF, microwave or otherenergy to the junction for ablation. Thus, in the embodiment of FIG. 29,cooling and heating (for ablating) occur at junction 210 and heat sinks212 extract heat from the ends of thermocouple elements 206 and 208nearest the heat sinks in the manner described above.

In FIG. 28, junction 210 is used for cooling only and heating forablation occurs at the distal cap 226. Distal cap 226 (which can be madeof any conductive and biocompatible material) is connected to wire 216which is connected to a separate energy (RF, microwave etc.) source. Inthis embodiment, heat sinks 212 also extract heat from distal cap 226.

Still other embodiments of the probe 200 are shown in FIGS. 30 and 31wherein heat sinks 212 are located along the "sides" of thermocoupleelements 206 and 208. As shown in FIG. 30, thermocouple elements 206 and208 are soldered together at their ends to form junction 210. At theiropposite ends, thermocouple elements 206 and 208 are connected to heatsinks 212 by wires 234. As shown in FIG. 30, heat sinks 212 are locatedalongside and parallel to thermocouple elements 206 and 208. Heat sinks212 are connected by wires 214 to an energy source (not shown) forproviding Peltier current to the heat sinks and thermocouple elements asdescribed above.

Probe 200 shown in FIG. 30 also includes a distal electrode (cap) 226which is connected to an ECG device via wire 236. In this embodiment andthe embodiments of FIGS. 28-29 and 31, additional electrodes (not shown)may be spaced along the probe or catheter body.

Thermocouple elements 206 and 208, junction 210 and heat sinks arelocated within carrier 204. Carrier 204 includes a passageway 238 forthe wires described above to extend through probe 200.

Junction 200 is connected to a separate energy source via wire 216 andto a temperature sensor wire 218. Thus junction 200 shown in FIG. 30 maybe cooled in accordance with the Peltier effect or heated (for ablation)by the separate energy source as described above. Heat sinks 212 assistin providing greater cooling at the junction and in controlling thetemperature of the junction during ablation.

In contrast to the junction shown in FIG. 30, the junction shown in FIG.31 is not connected to a separate energy source. In FIG. 31 (as in FIG.28), distal electrode (cap) 226 is connected to a separate energy sourcevia wire 236 and is used for ablation and some heat generated at distalelectrode 226 is extracted by the distal most heat sink 212.

In all other respects, the probe shown in FIGS. 31 operates in a manneridentical to the probe of FIGS. 30 described above.

As with the previously described embodiments, the probes shown in FIGS.18-31 may be used to map the electrophysiology of the heart and alsotreat the sources of electrophysiological disorders (e.g. arrythmia) byablation. In accordance with the present method, application of aPeltier current from an energy source through the heat sinks 212 andthermocouple elements 206 and 208 cools junction 210. As describedabove, cooling of the junction 210 when it is in contact with the hearttissue causes changes in the electrical impulses travelling through theheart. This allows the operator to "map" the heart and determine thelocation of the electrophysiological disorder as described above. Oncethe source of the electrophysiological disorder has been located, energyfrom a separate source is applied to the junction 210 to energize thejunction and, thereby, ablate the portion of the heart tissueresponsible for the electrophysiological disorder. (It should also beunderstood that the ablation energy can also be provided by thethermocouple elements in accordance with the Peltier effect as describedabove.)

Whether it is radiofrequency, microwave or other type, the energyapplied (and the resistance created at the point of contact between thejunction and tissue) will cause an increase in the temperature atjunction 210. While maximum power at the junction to provide foreffective ablation (i.e. deep lesions) is desirable, excessive heatingis to be avoided. Excessive heating of the junction and consequentwarming of the heart tissue can produce formation of clots and cause thecoagulation of blood at the point of contact between the junction andthe tissue. Formation of blood clots and coagulation can, in turn, causean electrical impedance which impedes the flow of the ablation energycurrent and results in the generation of additional and undesirable heatat the distal tip. Generally, a rise in the impedance typically beginsat temperatures of above 60° C. Thus, the heat generated at the junctionpoint must be controlled without sacrificing the ability of the energygenerated by the probe to penetrate the heart tissue and create, ifnecessary, deeper lesions.

The temperature of the junction may be controlled and an impedance riseprevented by reducing the energy applied to the junction by the RF,microwave or other energy source. Alternatively, the junction may becooled by introducing saline solution into the catheter at the point ofcontact with the heart tissue. In accordance with the present invention,if the catheter probe includes secondary thermocouple elements or heatsinks as described above, the ablating junction temperature may bemaintained within the desired range by extracting heat from thethermocouple elements connected to the junction.

More specifically, while the energy for ablation is continuously appliedto the junction from, for example, a separate energy source,simultaneous cooling of the junction takes place by continuousintroduction of current through the Peltier elements conductivelyconnected to the junction. The Peltier current allows for cooling of thedistal ends of the thermocouple elements and, thus, allows for coolingof the heated junction 210. As described above, as the distal ends ofthe Peltier elements are cooled, the proximal ends of the Peltierelements witness an increase in heat. The heat generated at the proximalends of the thermocouple elements is extracted by heat sinks 212 (orsecondary thermocouple elements as shown FIG. 11 and 13), thus keepingthe thermocouple elements cool and, consequently junction 210 within adesired temperature range. Of course, the Peltier current can also becontrolled to ensure that thermocouple elements are not cooled more thannecessary.

The method and apparatus for cooling the junctions as used in thepresent invention provides a more efficient alternative to the moretraditional methods and apparatus for regulating the temperature at thejunction. For example, regulating the temperature of the junction bycontrolling the amount of ablation energy to the junction requires thatthe energy source be turned off when, because of the increased energyrequired for deep penetration of the tissue, the temperature of thejunction approaches, more than, for example 60° C. This makes the entireablation procedure more time consuming. Application of saline, whilesatisfactory for cooling the probe tip, is also less efficient becausethe temperature of the saline also rises as it travels through thecatheter and, therefore, the saline is not as cool as desired when itreaches the distal probe tip. In addition, application of saline to thecatheter requires high pressures to effectively flush the catheter withsaline. The high pressure applied may cause the catheter to stiffen oreven move and possibly displace the junction from its desired location.Systems where saline is introduced directly to the point of contactbetween the distal tip and tissue are also less desirable becauseaddition of liquid to the heart should be avoided.

In sum, in accordance with the present invention, the Peltier effect mayused for evaluating, such as by mapping, the electrical activity ofheart, identifying the electrophysiological source of arrhythmia and, ifdesired, ablating a specific area of the heart tissue suspected of beingresponsible for the arrhythmia. Alternatively, the Peltier effect may beused for mapping and identifying the electrophysiological source ofarrhythmia or other cardiac disorder and a separate energy source (e.g.RF, microwave) may be used to ablate or otherwise treat the hearttissue. This allows the physician to use the same probe for bothidentifying the source of arrhythmia and treating it, and permitsmapping and ablating in one procedure without removing the catheter fromthe body of the patient.

Although the present invention has been described in terms of thepreferred embodiment as well as other alternative embodiments, variousmodifications, some immediately apparent, and others apparent only aftersome study, may be made without departing from the present invention.The scope of the present invention is not to be limited by the detaileddescription of the preferred embodiment but, rather, is to be defined bythe claims appended below.

That which is claimed:
 1. Apparatus for use in cardiac procedures, saidapparatus including an elongated body with a proximal end portion and adistal end portion, said distal end portion comprisingat least twothermocouple elements located within said distal end portion, each ofsaid thermocouple elements having a first end and a second end; saidthermocouple elements being conductively connected at said first ends ata junction; at least one heat sink conductively connected to the secondend of at least one thermocouple element; whereby application of avoltage across said thermocouple elements in accordance with the Peltiereffect affects the temperature of said junction.
 2. The apparatus ofclaim 1 further comprising an energy source wherein said junction isconductively connected to said energy source for heating said junction.3. The apparatus of claim 2 wherein said energy source providesradiofrequency energy to said junction.
 4. The apparatus of claim 1comprising a distal end cap conductively connected to and disposed oversaid junction.
 5. The apparatus of claim 4 wherein said distal end capis disposed over a portion of said thermocouple elements.
 6. Theapparatus of claim 4 wherein said distal end cap is made of silver. 7.The apparatus of claim 1 comprising at least two pole rings spaced alongsaid distal end portion.
 8. The apparatus of claim 7 wherein pole ringsare proximally spaced from said junction.
 9. The apparatus of claim 7wherein one of said pole rings is distally spaced from said junction.10. The apparatus of claim 7 wherein said pole rings comprise electrodesfor monitoring the electrical activity of the heart.
 11. The apparatusof claim 10 wherein said pole rings are made of a material selected fromthe group consisting of stainless steel and platinum iridium.
 12. Theapparatus of claim 7 comprising at least one annular groove in said bodyfor receiving said pole ring.
 13. The apparatus of claim 1 wherein saiddistal end portion comprises an angled distal tip.
 14. The apparatus ofclaim 1 further comprising a fixture for supporting said thermocoupleelements and said heat sink within said distal end portion.
 15. Theapparatus of claim 1 wherein said heat sink is made of a conductivematerial selected from the group consisting of gold and silver.
 16. Theapparatus of claim 1 comprising at least two heat sinks, each of saidheat sinks having a first end and a second end, wherein the first endsof said heat sinks are conductively connected to said second ends ofsaid thermocouple elements.
 17. The apparatus of claim 16 comprising asource for providing current in accordance with the Peltier effect,wherein said second ends of said heat sinks are conductively connectedto said source.
 18. The apparatus of claim 1 wherein said heat sink isat least of substantially comparable size to said thermocouple elementconductively connected to said heat sink.
 19. The apparatus of claim 18wherein said heat sink is greater in size than said thermocoupleelement.
 20. The apparatus of claim 19 wherein said heat sink isapproximately twice as long as said thermocouple element.
 21. Theapparatus of claim 1 wherein said junction is connected to a temperaturesensor.
 22. The apparatus of claim 1 comprising a first thermocoupleelement and a second thermocouple element wherein said firstthermocouple element is proximally located relative to said secondthermocouple element.
 23. The apparatus of claim 1 wherein saidthermocouple elements are disposed in a parallel arrangement.
 24. Theapparatus of claim 1 wherein said thermocouple elements have differingelectromotive potentials.
 25. A method for treating electrophysiologicaldisorders in the heart comprising:introducing an apparatus into theinterior of the heart, said apparatus having elements of differentelectromotive potential, said elements being conductively connected at ajunction; contacting the interior of the heart at a selected locationwith the junction; passing an electrical current through said elementsto reduce the temperature of the junction in accordance with the Peltiereffect and thereby cool the contacted heart tissue without damaging theheart tissue; monitoring for the effect of the cooling on the heart todetermine whether the source of the electrophysiological disorder hasbeen located; treating the heart tissue to substantially permanentlyinterrupt said source of the electrophysiological disorder byintroducing heat energy to said junction and thereby ablate said sourcewhile continuing to pass electrical current in accordance with thePeltier effect through said elements.
 26. The method of claim 25 whereinthe temperature of said junction does not exceed 60° C.
 27. The methodof claim 25 wherein the temperature of said junction prior to treatingsaid heart tissue is between 6 and 15° C.
 28. The method of claim 25comprising providing said electrical current from a first energy sourceand introducing said heat energy to said junction from an energy sourcethat is separate from the source providing said electrical current. 29.The method of claim 28 wherein said separate energy source comprises aradio frequency generator.
 30. The method of claim 28 wherein saidseparate energy source comprises a microwave source.
 31. The method ofclaim 25 comprising extracting heat from said elements.